Medium to large buildings are provided with an air-conditioning facility in a central air-conditioning system. Nowadays, the use of district cooling-and-heating systems is widespread, and such buildings are each supplied with hot water and chilled water from a cold heat source in a common district. The individual buildings are provided with an air conditioner which cools or heats the air inside of the building by taking air from the outdoor and regulating the air temperature using chilled water or hot water. In general, an air conditioner is controlled so that an indoor air temperature can be constantly maintained at a specified value regardless of variations in the outdoor air according to the seasons. In energy-saving technologies provided in public, an air conditioner is variously controlled according to the conditions of the outdoor air so that the consumption of chilled water or hot water can be reduced to the minimum.
Japanese Patent Laid-Open Publication No. 2014-59124 provides an air-conditioning control system which includes an air conditioner and a ventilation system provided separately from the air conditioner. The ventilation system makes a total heat exchange between outdoor air and exhaust air to regulate the temperature of the outdoor air, thereby saving the energy consumed in an air-conditioning facility.
Japanese Patent Publication No. 3990143 provides an outdoor-air cooling system which humidifies return air and mixes the return air with outdoor air. At this time, the volume of the outdoor air is controlled so that the temperature of the mixed air becomes equal to a supply-air temperature. This enables a chilled-water coil to stop operating, thereby reducing the energy consumption.